RtlSizeTMult - NtDoc

#ifndef _NTINTSAFE_H_INCLUDED_
#if WINAPI_FAMILY_PARTITION(WINAPI_PARTITION_APP | WINAPI_PARTITION_SYSTEM | WINAPI_PARTITION_GAMES)
//
// size_t multiplication
//
#ifdef _WIN64

#define RtlSizeTMult       RtlULongLongMult

#endif
#endif
#endif
View code on GitHub

#ifndef _NTINTSAFE_H_INCLUDED_
#if WINAPI_FAMILY_PARTITION(WINAPI_PARTITION_APP | WINAPI_PARTITION_SYSTEM | WINAPI_PARTITION_GAMES)
//
// size_t multiplication
//
#ifdef _WIN64
// ...
#else

_Must_inspect_result_
__inline
NTSTATUS
RtlSizeTMult(
    _In_ size_t Multiplicand,
    _In_ size_t Multiplier,
    _Out_ _Deref_out_range_(==, Multiplicand * Multiplier) size_t* pResult)
{
    ULONGLONG ull64Result = UInt32x32To64(Multiplicand, Multiplier);

    return RtlULongLongToSizeT(ull64Result, pResult);
}

#endif
#endif
#endif
View code on GitHub